This proposal seeks renewal of support for the infrastructure, personnel, and resources of the Mutant Mouse Resource and Research Center (MMRRC) at the University of California (UC) Davis (MMRRC-UCD). Since its inception 15 years ago, the MMRRC-UCD has been one of the primary mutant mouse archive and distribution repositories in the world. We are the largest of the 4 Centers in the MMRRC National Program, with an archive of over 30,392 mutant alleles representing ~93% of all live colonies, germplasm, and/or embryonic stem (ES) cells in the MMRRC system. The MMRRC-UCD has fulfilled nearly 4,754 orders from 3,214 investigators at 1,956 institutions in 23 countries. We have also been a leader in innovation and resource development for the system, introducing new products (e.g., targeted and gene trap ES cells) and initiating new services (e.g., blastocyst injection, ICSI, speed congenics) that have added scientific value to mouse models and enhanced utilization by the scientific research community of the MMRRC National Program. The MMRRC-UCD has leveraged its infrastructure and expertise to extend its service role by contracting with categorical NIH institutes (e.g., NINDS GENSAT project), biotechnology companies (Genentech and Lexicon), and several organizations (e.g., The Sanger Institute, Rockefeller University) to archive, distribute, custom breed, genotype, and phenotype 1000's of ES cell mutants and more than 1,500 BAC-transgenic, CRE, ENU-induced, and other mutant mouse collections. In addition, we have worked with the Centers and NIH program staff and developed and implemented advertising and marketing strategies, database management and informatics applications, website and online resources, customer and user services, operating procedures and policies, and shared governance of the national program. Thus, by archiving and delivering products and services effectively and efficiently, the MMRRC-UCD has established itself as a valuable scientific resource for the biomedical research community. Over the next 5 years, we shall focus our efforts on optimizing the quality of our resource, ensuring it relevance to individual users, and seeking maximum performance for the benefit of all whom we serve.